Modern starter devices are driven by electric motors which must be powerful enough to crank an engine. The energy source is usually a battery which will typically need to provide a current in excess of 200 amps at 12 volts to provide starting of an engine. In particular the starting of heavy diesel engines can require a power supply in excess of this.
In extreme conditions such as severe heat or cold or humidity, the battery and its associated electrical system can quickly become impaired. This is particularly true where servicing and maintenance are sub-standard or absent. Furthermore, in certain environments, electrically powered starters represent a fire hazard and, for example, the use of such starters in mines, is not permissible.
Mechanical starters provide a more reliable source of starting energy for internal combustion engines than electrically powered starting devices.
Mechanical starting devices hitherto employed typically comprise spring means for storing energy, means for applying energy to said spring means to store energy therein and drive means for converting said stored energy when released to provide a starting impulse for said engine.
In devices of the kind described, the spring means may comprise a bank of disc springs; the springs are strained by repeated manual rotation of a crank handle which rotates a worm on a shaft passing through the centre of said springs which worm is threaded through an end plate so that rotations of the worm moves the end plate to compress the discs. Once sufficient energy has been stored, the energy is manually released by disengaging a ratchet pawl. The spring reacts in an axial direction and the mechanism converts that axial movement into rotational energy. The rotational energy is directed to an output shaft which may include a pinion adapted to mesh with a ring gear carried on an engine flywheel.
Such known mechanical starters use a detachable crank handle to "wind up" the spring mechanism in order to store energy therein. These handles need to be of considerable dimension in order to apply the necessary energy and to provide the necessary mechanical advantage for the operative. This in turn limits the positioning and orientation of the starter to a position which allows free access of the crank handle and easy access generally to that part of the engine.
Compression ignition engines such as diesel engines are particularly amenable to starting by such mechanical devices because they do not require in the normal course of events the associated electrical system to maintain them in operation. Furthermore, the amount of rotation available to a mechanical starter is limited by the travel of the disc springs in the time period before the stored energy is exhausted. In starters currently available, the spring travel is small and short lived. They are, thus, most successful for use with multiple cylinder diesel engines where a combustion event is likely to occur over the arc of rotation of the crank shaft induced by the starting device.
As stated above the spring energy of the disc springs is released as an axial motion which has to be converted to rotational motion to be useful in the starting of an engine. The energy losses involved in the conversion processes are significant and furthermore such a motor must be heavily engineered to be able to withstand extremely high axial forces exerted by the springs. This adds to both cost and weight, to such an extent, as to make their use at a premium.
There is, therefore, a need for a mechanical starting device of improved efficiency and versatility which enables the starter to be used to start a wide range of engines. There is also a need for a mechanical starting device having reduced weight and being of cheaper construction. There is a further requirement for a starting device which is convenient to operate and does not require, of necessity, a crank handle of large throw.
U.S. Pat. No. 3,127,883 seeks to provide a solution to this problem and the primary aim of the invention described therein is to provide an improved spring starter motor that is efficient and safe. More specifically, it is an object of the invention to provide an improved starter motor which cannot be accidentally tripped when wound and which has no projecting parts which are driven during the starting operation.